(207g) Two-Step Selective Bromination of Thiophenic Compounds for Gasoline Desulfurization Under Mild Conditions

The removal of trace amount of refractory thiophenic
compounds from fuels has raised intense concern globally. The development of
less energy-intensified desulfurization process is under great demand. In this
work, we proposed a new approach of two-step selective bromination of
thiophenic compounds for gasoline desulfurization under mild conditions. The Ag
modified MoO₃ nanorods (AMO) were synthesized and
characterized by XRD, HRTEM and N₂ adsorption, and evaluated in selective
bromination of thiophenic compounds. Results showed that (a) thiophenic
compounds in model gasoline can be selectively brominated over AMO catalyst
with the addition of Br₂, and their bromination production can be
removed selectively by followed-up extraction. (b) At the optimized Ag loading
of 10%, the apparent rate constants for T and BT reached as high as 95.8h^-1
and 142.7h^-1, respectively under ambient conditions, much higher
than those cases in oxidative desulfurization, adsorptive desulfurization, etc.
Product analyses showed that the portion of dibromo-thiophenes increased dramatically
with increasing loading of Ag, due likely to the formation of MoAg₂O₄.
(c) The bromination selectivity of thiophenic compounds reached four orders of
magnitude than those of aromatic compounds in fuel. Meanwhile, the competition from
olefins can be strategically suppressed by HBr pretreatment. (d) With the
integration of the 2^nd-step of extraction, desulfurization capacity
of thiophenes reached as high as 30 mg-S/g-cat, while the integrated system
showed excellent bromination desulfurization capacity of thiophene at ~260 mg-S/g-cat
under high fuel-to-catalyst mass ratio of 5000. The adsorption of various
bromides over MoAg₂O₄ was simulated to elucidate the desulfurization
mechanism. The fast kinetics, high desulfurization capacity and selectivity of
the proposed two-step approach under mild conditions make it promising for
gasoline desulfurization.

Keywords: desulfurization, gasoline, selectivity, Ag
modified MoO₃